(China Plus) The alleged "UFO" seen in the sky above northern China on Friday evening was a noctilucent contrail, says the Chinese Academy of Science (CAS).
Noctilucent roughly translates from Latin to mean "shining at night."

A noctilucent cloud crosses the sky of northern China on Friday, April 27, 2018. [Screenshot:Wechat/tjjwbwx]

According to a post published Saturday on the CAS WeChat account, the cloud was spotted in several northern cities, including Beijing, Tianjin, Zhengzhou, and Qingdao. Photos of the cloud formation went viral on social media in China, with some netizens saying that it could have been caused by a UFO, a satellite launch, or a military exercise.

CAS explained that the cloud was actually a type of condensation trail. The line-shaped clouds are produced by aircraft engine exhaust, or changes in air pressure.
CAS says this contrail had its unusual appearances because it formed in the upper atmosphere where the clouds are still reached by the day's sunlight, but the sun is below the horizon for observers. This characteristic is what sets "noctilucent" clouds apart.
Although the cloud formation was popular with observers, CAS warns that noctilucent clouds are regarded as a sign of global warming.